Board -- where your pins (content you’ve posted) are displayed; similar to Facebook Groups and Twitter Lists, a means of organizing your pins by theme or whatever parameters you choose

Like -- (n) an option on pins that allows users to show their agreement with/approval of/positive response to said pin
(v) the act of selecting that option to openly show your agreement with/approval of/positive response to the related pin; doing so adds the pin to your profile's like section

Pin -- (n) a piece of content you have posted to one of your boards on Pinterest
(v) the act of posting a piece of content to one of your boards on Pinterest

Pinner -- a Pinterest user; shorthand/slang
note: users (Pinners) can mention and follow other Pinners in much the same manner as Twitter:

• mentions - formatted @username (like Twitter)
• follow - Pinners can follow other user’s individual boards (selecting follow under the individual board) or all of their boards (selecting the follow all option on a their profile page)
  

Repin -- the act of sharing another user’s pin on one of your boards; analogous to a ‘retweet’ on Twitter; differs from liking a pin, which only adds the pin to your profile’s like section, repinning allows you to place the pin on one of your boards as well as edit the description; the original source-link of the pin does not change, regardless of the number of repins

Secret Boards -- they are what you think they are – private boards for your eyes only; activity on those boards does not show anywhere else on Pinterest; existing boards can not be made secret, as others may have already repinned from that board