Padma is the Lotus, also called Kamala.

The lotus is associated with spiritual purity as it is rooted in the mud, but untouched by the mud, it blooms flawlessly on the surface of the water. Man should also guard against spiritual pollution.

Krishna says in the Bhagavad Gita, chapter V, verse 10
He dedicates all his actions to me and carries them out without intention.
So he remains untouched by action, like the lotus blossom by water.

Vishnu is also called the lotus-eyed one. In the creation myth a lotus sprouts from his navel, Padmayoni, on which Brahma, the creator, sits, in this appearance Vishnu is called Padmanabha.

The Lotus is an insignia of Vishnu. See also Vishnu’s Insignia.