What is the difference between a senior minister and a pastor?

In the Catholic Church, and in some other churches with a 'catholic' character, 'priest' is one of three orders of ordained ministry (bishop, presbyter/priest, deacon). 'Pastor' is the title, and job description, of a priest who is given responsibility for a parish.

Not all priests are pastors, and not all ministers are priests. Sometimes, the person given the job of pastor is not a priest, and is usually given a different title, like 'pastoral life coordinator' or 'pastoral administrator' (cf, CIC 517.2).

In many evangelical churches, all ordained ministers are called 'pastor', (youth pastor, children's pastor, worship pastor, etc) and the pastor given responsibility for a parish or congregation is called the 'senior pastor'. Some churches only consider one order of ordained ministers, which may be called pastors or ministers.