The House has the power to punish breaches of its privilege or contempts.
There’s no single definition of what constitutes a breach of privilege or a contempt. Very broadly speaking, a breach of privilege is an attempt to interfere with one of the unique rights and powers that belong to Parliament and a contempt is a bit like a contempt of court. All breaches of privilege are contempts, but not all contempts are breaches of privilege. For example, if someone were to obstruct an MP in carrying out their role that might necessarily not be a breach of privilege but it could be a contempt.
The House decides on breaches of privilege and contempts on a case-by-case basis, on the advice of the Committee of Privileges, a cross-party select committee of MPs that considers matters relating to privilege referred to it by the House.
An example of something that could be a breach of privilege is the leaking of a draft report from a select committee. An example of something that could be a contempt is refusing to appear before a select committee.