Facial expression adopted by metal bands in those photos with all the members stood in a line which they all seem to have in abundance. Illustrated perfectly by this emote: -_- , the metal stare conveys deep fiery slightly intimidating meaningfulness. The -_- face is accompanied by a leaned back pose, sometimes with arms folded.
The Metal Stare is universally used by heavy metal bands and to a lesser extent by bands of other genres. A more popular version used in other genres is a more wide-eyed look with the head slightly tilted down, giving a more quirky, almost disapproving-looking feel that tells you "this guy is a lively interesting non-conformist chap".
Photographer: "Great boys you're beautiful now give me a Metal Stare..."