Isoelectronic point is usually defined for amino acids.

Amino acids have an amino and carboxylic group

The carboxylic group forms an anion and the amino group forms a cation. Therefore, amino acids are of two types: anionic and cationic. The $pH$ at which a particular molecule carries no net electric charge is known as isoelectronic point When the anionic and cationic charge is contained within the same molecule, it is known as the Zwitter ion.

Zwitter ion exists at isoelectronic $pH$

Therefore, at isoelectronic $pH$,

$1.$ Net charge is zero (As the cationic and anionic charge is equal)

$2.$ Concentration of cation and anion are equal

$3.$ Maximum concentration of zwitterion is present

Below is the example of the zwitterion