Limited Edition Prints are Prints produced by or on behalf of the artist where a stated maximum number can only be made.
They are numbered either on the print or on a separate certificate so you know where along the print run your edition of the print comes.
For example 2/250. This means that your print is the 2nd print to be made out of a total of 250 that can potentially be made.
The no. 1 is the best number to have.
Any printing method can be used to produce a limited edition, although with methods like digital Giclee printing, it is far easier for artists to produce smaller runs or even one offs.
An Open Edition print is one that can and will be printed continuously.