Taken exactly as stated there is no meaning because of the obvious syntax error: there should only be two semicolons within the brackets. i & lt is valid C; it performs a bitwise AND of i and lt, so it looks like you have four clauses within the brackets, which is incorrect.
However < is HTML code for the less than sign, so probably this should read
for (int i=0; i<20; i++)
in which case there is no error (apart from the missing loop body), and the meaning of the statement is to loop i from 0-19 inclusive.