הלכה על שבת 236:14

The main part of Pesukei De-zimra is the last six psalms in Tehilim (145-150), the most important being the first (145, “Tehilla Le-David”). Customarily, this psalm is introduced with the verses beginning with the word “ashrei,” and that psalm is therefore generally referred to as Ashrei. The other five psalms each starts and ends with the word “Halleluyah,” about which R. Yossi says, “May my portion be among those who complete the Hallel every day” (Shabbat 118b).