To be quiet means you don't make any noise. When you’re trying not to wake a sleeping lion, you will be quiet when you run by it.
The versatile quiet, which can be a noun, adjective, or verb (to quiet others), is one of those words that is best understood through its antonyms — loud or hectic. Let a marching band practice in your apartment, and you will long for a little quiet. Quiet is one of those words that thankfully follow the "i" before "e," except after "c" spelling rule.
characterized by an absence or near absence of agitation or activity
a period of calm weather
make calm or still
with little or no activity or no agitation (`quiet' is a nonstandard variant for `quietly')
free of noise or uproar; or making little if any sound
the absence of sound
become quiet or quieter