Peer Check (or Cross Check) means that that I look out for the team and am not afraid to ask questions if I think someone has made an error. It also means that we, ourselves, are willing to be checked.
Look out for your team members.
Offer to check the work of others
Example:
Second check a calculation, proofread a memo, offer to help a team member with their work.
Point out work conditions (hazards) your team members might not have noticed
Example:
A floor that recently was mopped, a trip hazard in the lobby.
Point out unintended slips and lapses
Example:
A supply room key left on the counter, an order placed in the wrong chart.