What does waived/injured mean in the NFL?

Waived injured means the team is releasing the player but the player is injured. The team is responsible to pay the player until his injury has healed. Other teams are allowed to pick up the player that was Waived Injured, but they are doing so knowing that the player is inured and not able to play.

To expand on the existing answer (as there appear to be more reference articles available on the internet since the original question was asked e.g. here ).

The waived/injured designation is only available to be used on players who are not vested veterans (i.e. they have less than four accrued years). These players are not being really being cut/released as they will be subject to waivers (a process where other teams, in a set order, have the opportunity to claim the player at his existing contract value) and if they are not claimed they will be placed on the teams injured reserve list (IR).

Prior to roster cut downs (shortly before the season starts each year) this is the only way for an injured player with three or less accrued years to be placed on a teams IR; they cannot simply move him there, other teams have to have the chance to claim him. After cut down a team may still use the waived/injured designation (presumably if they are hoping another team will claim him and save them any salary they are still liable for) or place him directly on IR.

Once the player is on IR then (from source above):

After a player is waived/injured, the player and the team have five days to agree to an injury settlement. An injury settlement is designed for a team to pay the player for the time he is expected to miss with the injury.

If a settlement is reached, the player becomes a free agent and can sign with another team immediately. If a settlement is not reached, the player goes on the team's injured reserve. A player on IR can't be waived until he passes a physical.