What is meant by Hydronium ion?

Definition for Hydronium ion:

• It can be formed by the combination of a H⁺ ion with an H₂O molecule.
• Its chemical formula is H₃O⁺.
• It is composed of three hydrogen atoms and one oxygen atom.

Hydronium ion formation:

$H^{+}\left(aq\right)+H_{2}O\left(l\right)\to H_3{O}^{+}\left(aq\right)$