The term 'expert, in slang' can be expressed in three different ways: WHIZ (4 letters), wiz (3 letters), and PRO (3 letters). WHIZ is a slang term for an expert or someone who is very knowledgeable in a particular field. Wiz is another slang term for an expert or someone who is highly skilled in a certain area. Lastly, PRO is a slang term for an expert or someone who is experienced in a certain activity. All three terms are used to describe someone who is an expert in their field.