what does it mean in chemistry in bond line notation - a circle?

Question

bond notation was like this : ...
...
....... ... .......
...
circle

Answer 1

you see the circle mainly in cyclic compound like benzene or aromatic hydrocarbons. This means that a given number of electrons (6 if the cycle is hexagonal) are not localized between two atoms but belong to the whole cycle. this gives peculiar properties.
For benzene there was a old representations showing the hexagonal cycle with 3 double bounds.That representation is erroneous and can lead to mistakes. The correct representation is the circle

Answer 2

There are occasions when it is important to be able to show the precise 3-D arrangement in parts of some molecules. To do this, the bonds are shown using conventional symbols:
___ a straight (dark) line usually denotes bond in the plane of paper, a dotted line ............ indicates bond going back into paper - away from you and a wedge (pointed towards one atom and broad towards other) indicates bond coming out of paper towards you.
There are many conventional symbols like this, for example, pi bond is indicated by double lines, multiplicity of bonds distributed over structure (as in Benzene) by circle, different signs for Tau bond and sigma bond, covalent bond, ionic bond etc.

Answer 3

"maussy" makes sense and is correct.