The term Committee of the whole House means that a Bill can be discussed in detail by all Members. In the Commons this usually takes place in a Public Bill Committee, outside the Chamber, but occasionally a Bill will be considered in a Committee of the whole House in the main Chamber. Any Bill can be referred to a Committee of the whole House but the procedure is normally reserved for finance Bills and other important, controversial legislation. In the House of Lords the committee stage of a Bill usually takes place in the Lords Chamber and any Member can take part. The Committee may choose to vote on any amendment and all Members present can vote.
Further information on this subject can be found from the following links.
About Parliament: Bill stages
About Parliament: Committees