What is the meaning of Waiver_wire?

a league-wide list to which an inexperienced player is added for a short period when cut from a team's roster; any team in the league may make a claim for the player during the period, at the end of which the lowest ranking claimant has right of first refusal, or the player may become a free agent if unclaimed

a similar period during which managers can claim a player, with successful claimants decided in various ways depending on the league.

Source: wiktionary.org