Circle
white circle
$\circ$
\circ
It is derived from the circle.
black circle
$\bullet$
\bullet
It is derived from the bullet point used in bullet lists.
big circle
$\bigcirc$
\bigcirc
By adding the "big" to certain commands, you can increase their size.
circle and plus
$\oplus$
\oplus
A "+" sign is placed inside the letter "o".
circle and minus
$\ominus$
\ominus
A "-" sign is placed inside the letter "o".
circle and times
$\otimes$
\otimes
A "times" (multiplication symbol) is placed inside the letter "o".
circle and dot
$\odot$
\odot
A dot is placed inside the letter "o".