The tiny bumps that appear on the skin from cold, fear, strong emotion, etc.; commonly used in the expression '鳥肌が立つ' (to get goosebumps).
怖い映画を見て鳥肌が立った。
I got goosebumps watching a scary movie.
そのピアノ演奏は感動的で鳥肌が立った。
That piano performance was so moving I got goosebumps.
冷たい風に当たって腕に鳥肌が立った。
The cold wind hit me and I got gooseflesh on my arms.