If you're not familiar with the term "career summary," it's those few lines or bullets at the top of your resume directly under your name and contact information that tell an employer who you are. Some call it a career profile or executive summary, among other things.
Before we go on and talk about what it is, let's talk about what it's not. It is not an objective statement. There is a very important distinction between the two. If you've been in the workforce for a long time, you're probably more familiar with an objective. That's old news. An objective would tell an employer what you were looking for. Employers now receive so many job applications that they expect you to do a bit more work to tell the employer that you are what they are looking for.