Now I Get It: What is a continuing resolution?

The government shutdown officially ended on its third day after overcoming a major hurdle in the Senate. GOP Senate Majority Leader Mitch McConnell and Democratic Senate Minority Leader Chuck Schumer agreed on a compromise. Schumer pledged his support for the spending bill in exchange for McConnell's promise that they would work on legislation to prevent young undocumented immigrants from being deported. The stopgap spending bill is a short-term solution known as a continuing resolution, or C.R., but what is that?