The phrase "critical part" refers to an essential or important component of something. It is a key element that plays a crucial role in the overall functioning or success of a system, process, or object. Full definition
Many lawyers who write law blogs miss the most critical part of writing a legal blog — catering to their audience. (legalmarketingreview.com)
Teaching your puppy where you expect him or her to go to the bathroom is probably the most critical part of training. (homevet.com)
Little data existed to show the real value brought by retailers, breeders and others who play critical parts in connecting pets with animal lovers. (petbusiness.com)