A backbencher is a member of Parliament who is not a minister or shadow minister. Backbenchers have important roles drawing attention to issues in their electorate or state/territory by speaking about them in the Parliament, and debating and voting on bills (draft laws).
If a backbencher is a member of the government or opposition, they may also be a member of a backbench committee. These committees are not official parliamentary committees but informal groups of backbenchers from the same team. Backbench committees undertake a range of jobs, such as investigating a bill or researching a topic to provide information to their team members.