What is a plasmid and why it is important to the genetics of many bacteria?

and the plasmid is so important because its used for transfection. you put in it a DNA sequence for the gene you are intrested in and you inject it into the bacteria so it replicates and you have the expression of the gene.

It’s circular DNA peaces present only in bacteria beside chromosomal DNA and it's very important for bacteria because carried antibiotic resistant and virulence factor determinants.