Stands for "Point to Point Protocol." It is the Internet standard for dial-up connections. PPP is a set of rules that defines how your modem connection exchanges packets of data with other systems on the Internet. Basically, if you have an ISP that you connect to via modem, you're most likely using PPP.
Meaning of PPP in English
English glossary of computer and Internet terms. Английский глоссарий компьютерных и Интернет терминов. 2012