What does percent yield mean in chemistry?

is the ratio of the actual yield to the theoretical yield. (If it is over 100% it means something went wrong.)

##"Percent yield" = "actual yield" /"theoretical yield"##

The actual yield is a product that is obtained by experimentation. The theoretical yield is obtained through stoichiometric calculation.

If the two yields are equal, you have 100 % yield.

Usually you obtain less than 100 %.

It is impossible to obtain a yield greater than 100%. If that happens, some experimental error must have occurred in the creation of the desired product, actual yield.