MRCP is Membership to the Royal College of Physicians. This is awarded when a candidate has passed their PACEs exam, which is the last of three exams required to achieve MRCP.
You may see jobs advertised which state a requirement for MRCP or PACEs, and this means they are looking for a doctor who has passed PACEs and therefore has MRCP.
It may be very confusing how the MRCP exams sit alongside the PLAB exams. Our friends at Road to UK have laid out the pros and cons of taking the various exams in an excellent article here. You will have to create a free account with Road to UK to see this article, but you will find so much helpful information on their website about moving to the UK to start an NHS job, we recommend joining their community anyway.
If you decide to take the MRCP exams, there are exam centres all over the world. On this page you can read about where these centres are located (including UK centres), the dates and the costs associated with the exams.