A "field" is an area of study and work. Some examples of "fields" include:

• the field of accounting
• the medical field (doctors, nurses, etc.)
• the field of education

A field is similar to an "industry". An "industry" is an area of business. Here are some examples of industries:

• the automotive industry (building and selling cars)
• the hospitality industry (hotels)
• the entertainment industry (movies, TV, and music)

A "competitive" field is one that a lot of people are trying to get jobs in. Acting, professional sports, and veterinary medicine are examples of very competitive fields in the U.S.