LP are Lagrange Points. They occur around gas giants, and act as in-system jump points.
And are why hyperdrives are not nearly as useful as they used to be. Useful LPs are those which occur both in a primary and a distant companion that would take a year to travel to conventionally. Hyperdrive allows 10x speed outside the hyperlimit (which can be displayed by checking a box in the F3 screen). You'll see LPs as targets for move orders in the F12 screen - selecting one brings up a sub-dialog which lets you pick another LP in the system to jump to.
Note that a lot of systems have non- (or marginally-)useful LPs - only 1, or 2 or more around the same primary.
John