front line

noun
  1. 1

    A front, or a boundary between opposing positions.

  2. 2

    A site of a conflict, effort, or controversial matter of any kind.

  3. 3

    The site of interaction with outsiders, such as customers.

  4. 4

    A low level.

  5. 5

    Attack, collectively the attackers or forwards.

Synonyms

Antonyms

Source: https://en.wiktionary.org/wiki/front%20line