The conditional jump instructions execute a near (same segment)
jump if and only if their conditions are satisfied. For example,
JNZ jumps only if the zero flag is not set.
The ordinary form of the instructions has only a 128-byte range; the
NEAR form is a 386 extension to the instruction set, and can
span the full size of a segment. NASM will not override your choice
of jump instruction: if you want Jcc NEAR, you have to use the
NEAR keyword.
The SHORT keyword is allowed on the first form of the
instruction, for clarity, but is not necessary.
For details of the condition codes, see the condition codes.