Definition of terms used in the ".theme" files

Hello,

I very much enjoy tweaking the themes that come with Bear. I would be grateful if someone would have the patience to explain the meaning of the terms below.

thanks in advance for your time and help

"text secondary color": "#888888",
"text tertiary color": "#7c7f93",
"background secondary color": "#E3E3E9",
"background tertiary color": "#D4D4DA",
"stroke color": "#D7D7DD",
"accent color": "#84464F",
"search primary color": "#ACD7EB",
"selection color": "#D2DFE8"