I come across the term while blog hopping though the term is not alien to me but the deep meaning of it i still have to find it.   So while uploading pics, i tried to google yeast infection and this is what i gathered.

What is yeast infection?
A yeast infection is  also known as candidiasis, and it’s the name for a common infection caused by a yeast called candida albicans (a type of fungus).  It usually occur in warm, moist parts of our body such as the mouth and moist skin.  Yeast infections usually occur in warm, moist parts of the body, such as the mouth and moist areas of skin and most likely the vagina. When they cause an infection in the vagina, it is known as vulvovaginal candidiasis.  In other words, normally yeast as fungus lives in the vagina in small numbers.  But when pH is altered they grow up into big big numbers.

What are the symptoms?
- itching and irritation in the vagina
- redness, swelling, or itching of the vulva (the folds of skin outside the vagina)
- a thick, white discharge that can look like cottage cheese and is usually odorless, although it might smell like bread or yeast
- pain or burning when urinating or during sex

Is Vaginal yeast infection treatable?  Yes

Can it be prevented?  Yes and there are some simple ways to be done to prevent having an infection -

-Wear cotton, not nylon, underwear, and avoid tight-fitting pants and panty hose.
- Change out of a wet swimsuit right away.
- Avoid douches and feminine sprays, scented toilet paper, and deodorant tampons.

 What i like to note is that — yeast infection can happen to any girl and is not sex related.  Although it can be spread to your partner.  Guys can also have the infection but is not called vagina yeast infection but is called – balanitis.

More about YI:
http://women.webmd.com/tc/vaginal-yeast-infections-topic-overview
http://kidshealth.org/teen/sexual_health/stds/yeast_infections.html