Avoidant attachment is one of the insecure attachment patterns adults carry out of their earliest relationships. Attachment researchers describe everyone along two dimensions: how much anxiety you feel about being left, and how much discomfort you feel with closeness. Avoidant attachment is the high end of that second dimension. Where an anxious person under stress moves toward their partner, an avoidant person moves away, not because the relationship does not matter but because closeness itself raises the internal pressure.
In daily life the pattern is unmistakable once you can name it. Needing room right after the best weekend. Going quiet in a conflict instead of louder. Handling hard things alone first and mentioning them later, if at all. Partners usually describe the same wall from the outside: warm, then suddenly out of reach, with no explanation attached.
Estimates vary by study and measure, but somewhere between a fifth and a third of adults lean avoidant, which makes it the most common insecure pattern. That number hides the most useful fact about the word, though, and the next section is the reason this page exists.