What is Friday the 13th uncut?

The definition of 'uncut' just means they left in some deleted scenes that weren't in the original version.
Friday the 13th uncut is an alternate version of the film Friday the 13th, also sometimes referred to as the 'directors cut' version. It means that it is unedited/uncut. Any scenes that were cut from the original film's theatrical release have been added back in to the uncut version.