The term "nobrainer" refers to a decision, choice, or action that is so obvious or easy that it requires little or no thought. Essentially, it's something that is straightforward and doesn't necessitate deep consideration or analysis. When someone says something is a "nobrainer," they imply that anyone would easily come to the same conclusion without much effort.
The word "nobrainer" is a compound of "no" and "brainer." The prefix "no" indicates the absence of something, while "brainer" suggests that it would typically require thought or consideration. The term emerged in informal language in the latter half of the 20th century, often used in casual conversation to denote simplicity in choices or decisions.