Psalms 100:1

וַמִזְמוֹר לְתוֹדָה הָרִיעוּ לַה' כָּל הָאָרֶץ

A Psalm of thanksgiving. Shout to Hashem, all the earth.

Continuing pesukei d’zimra, the morning verses of praise

Rashi tells us that this Psalm was recited in the Temple when a korban todah (thanksgiving sacrifice) was offered. Nowadays, we recite it in lieu of the korban todah. Accordingly, this Psalm is not recited on days when the korban todah was not offered, such as on erev Pesach.