Experienced users, please keep all of this in mind when helping newbies, especially those who explicitly say they're not native speakers of English.
If you haven't found what you're looking for, try Wikipedia, simple English wiki or urban dictionary (for slang or colloquial terms, including abbreviations). And don't be too shy to ask!
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edit: A couple of new quick explanations:
AF=Aunt Flow or Aunt Flo, meaning period/menstruation (follow the link for more slangy synonyms)
IUD (coil), NuvaRing, HBC and "the pill" refer to various types of contraception.
The amount/volume of blood that a cup can hold. The three main factors affecting it are the dimensions, placement of holes and shape. (Wide, rounded cups like the large Fleurcup or Meluna XL have the highest capacity)
The organ between the uterus and the vagina, also known as the neck of the uterus.
See also: introductory post (including the difference from the hymen), Beautiful Cervix Project (graphic photos)
A "dangly" cervix is one that dangles (hangs) into the vagina.
CLOTH PADS AND LINERS
also known as: reusable pads, washable pads
Pads that can be washed and used again. Nowadays they are good quality and available commercially, mostly from small businesses. Many also make their own cloth pads. The different styles are explained here.
also known as: going #2/number two, pooping, sh*tting and many other terms
The scientific term is bowel movement.
"Going to the toilet/bathroom" can also mean urination; simply saying "going" often implies defecation.
May warrant a TMI warning.
also known as: measurements, size
The length and width of a menstrual cup, preferably in millimeters (mm) rather than inches. The specific numbers can matter surprisingly much, and what a company calls "large" or "small" is far less important. For precision, it's better to use the word "size" only referring to each company's options, not the exact dimensions.
Menstrual products that are used once and thrown away (disposed of), like most pads and tampons. The only disposable kind of cups are the Insteads, and even they offer a reusable option as well.
GRAPHIC, NSFW (not safe for work), not safe for school, nsfw warning
NSFW is an abbreviation for warning about pictures that are inaproppriate for public computers, such as those at work or school. Remember to use an LJ cut if you post them, and place the warning before the LJ-cut. Also note that graphic images are generally NOT diagrams, but detailed and NSFW. "Graphic texts" are vivid and may warrant a trigger warning.
A piece of tissue that may hide/cover the entrance to the vagina. It's often considered something binary, but in many cases it's not a simple "yes or no" question.
Sometimes a hymen can be seen with a mirror. It's well-known that the hymen generally has a hole in it - large enough to insert at least one finger. If you feel something inside with a tiny hole in it, that's likely to be the cervix.
Further info | about "tightness"
The virgin's guide to cups
LEAKS, OVERFLOW, RESIDUAL SLOBBER
A leak happens when blood doesn't go into the cup when it should. An important distinction is leaks vs overflow. The latter is what happens when a cup is simply too full - either due to having a low capacity or because the cervix sits in the cup. (If your cup is never completely full, your cervix is taking some space)
Residual slobber is a separate problem. It may look like spotting or even serious leaking, but the real cause is the blood that remains in the vagina during removal/reinsertion.
Timing: residual slobber is more or less immediate and ends after some time, overflow begins after a few hours, leaks can be constant or correlate with external factors like activity, body position, bowel movements etc.
PADS, SANITARY PADS, LINERS, PANTY-LINERS
also known as: sanitary napkins or sanitary towels
The most common way of external menstrual protection. Can be reusable or disposable.
Liners are a type of thin and narrow pads used for spotting, as back-up to a menstrual cup, when you're not menstruating etc.
POPPING OPEN, unfolding
When a cup opens in the vagina after being folded. Note that it's normal not to have a popping sound or sensation. The earliest cups were stiff, whereas with soft cups the process is often more slow and gradual; it may take more time to learn.
The time after giving birth to a child. When one is not allowed to use tampons post-birth, cups should NOT be used either. Cloth pads can be used safely and there are special ones for post-partum bleeding.
Menstrual products that are washed and used many times: cloth pads, menstrual cups, sponges etc. The opposite of disposable.
SEAL AND SUCTION
See this post. You have a seal when the cup is open and rounded/slightly oval, sitting (O) around your cervix or directly below it.
Generally it means a very light bleeding, literally when you get spots on your underwear or pad. Unlike tampons, cups can be used for this type of bleeding, except for the time of pregnancy and post-partum.
Spotting is also commonly used to refer to minor leaks or residual slobber.
The handle at the bottom of most cups, often like a stick/flower stem. Some companies offer unusual stems, most notably Meluna.
The dimensions generally don't include the stem, unless the company doesn't provide the information.
Unlike a tampon string, the cup stem shouldn't generally stick out.
The quality of a cup being stiff (hard) rather than soft. You can use the stiffness chart to choose a stiffer or softer cup and find out more about the benefits and possible disadvantages of both.
TMI (too much information), tmi warning, trigger warning, tw
An abbreviation for warning about details that follow, especially unpleasant ones. It's generally agreed that nothing vagina-related is TMI here, but if you post about defecation and cup use, remember that someone may be eating when they see your post. Additionally, some topics can be triggering (upsetting), so consider using a trigger warning if you post about helping a rape survivor use cups, "giving birth" to your cup or something that may trigger a blood phobia.
also known as: going #1/number one (as opposed to number two), peeing
May warrant a TMI warning.
also known as: vag, vajayjay, hoohah, "down there" and many other terms, most of which are inappropriate here (and personally I would encourage everyone to just say vagina and not be shy/squeamish about it)
from wiktionary: [the word] vagina is often used to refer to the vulva or female genitals generally, even though strictly speaking the vagina is a wholly internal structure.
A menstrual cup should be worn completely inside the vagina. Unlike a tampon string, the cup stem shouldn't generally stick out.
See also: cervix, hymen, NSFW photos
The external genital organ often confused with the vagina. From wiktionary: calling the vulva the vagina is rather like calling the lips the mouth or throat.
Thank you for reading. This glossary or parts of it can be used and edited freely for non-commercial purposes.
Originally written for http://menstrual-cups.livejournal.com
© Marina Jevdokimova (Serpent), 2015. Please include this disclaimer when copying.