What are bitcoin no deposit bonus codes?

Could you elaborate on the concept of "Bitcoin no deposit bonus codes"? Are these codes offered by specific cryptocurrency exchanges or platforms? Do they allow users to receive Bitcoin without making an initial deposit? If so, how do they work? Are there any conditions or restrictions attached to these bonus codes? Furthermore, are they safe to use, and how can one ensure they are not falling for a scam? I'm particularly interested in understanding the mechanics and implications behind such offers.