Pre-cum is the slang term for pre-ejaculatory fluid. Pre-ejaculatory fluid is clear. It’s released from the penis during arousal and helps line the urethra to protect sperm that could travel down during ejaculation.
There may be sperm in the pre-ejaculate fluid. Sperm from a previous ejaculation can remain in the urethra, and then the ‘leftover’ sperm will come out the urethra in the pre-ejaculate fluid.