Not-related word found in a group of words is called ODD Word.
Apple, Onion, potato, Brinjal : In this set of words, onion, potato and brinjal are the names of vegetables. Whereas the APPLE is the name of a fruit. So, APPLE is the odd word out.
Temple, church, mosque, palace : In this set of words, Temple, church and mosque are the name of worship of various religions. But the word PALACE is not the name of worship. So, the word PALACE is the odd word out.