crystal clear

Short definition from Wiktionary

Adjective

1. 1
   Completely clear (in various senses): Without ambiguity or doubt; completely understood.
2. 2
   Completely clear (in various senses): Visually clear, a sharp image, of high acuity.
3. 3
   Completely clear (in various senses): Very translucent or transparent.
4. 4
   Completely clear (in various senses): Having no clouds.
5. 5
   Completely clear (in various senses): Aurally clear.
6. 6
   Alternative form of crystal clear.