The House of Commons and the House of Lords communicate with each other by means of a message.
When consideration of a bill is completed in the House of Lords, for example, a message is sent to the Commons to let MPs know.
Messages are also exchanged between each House to inform MPs and peers of progress on reports and other parliamentary documents.
Messages are carried from one chamber to the other by one of the Clerks of the House.
Parliamentary business can be interrupted when a message arrives so that it can be discussed immediately - but it is more normal for a message to be considered at a later date.