John Hilber, Grand Rapids Theological Seminary Old Testament Professor, writes about the section of the Psalms known as the Psalms of Ascents:
Psalms 120-134 are unified as a sub-collection of the Psalter by the common title “A song of ascents.” The background to this superscription has several interpretations. The Hebrew word translated “ascents” is related to the verb “to go up.” Since the Jerusalem temple is geographically situated on a hilltop in the south-central mountain region of Israel, going to Jerusalem involved an “ascent.” Ezra refers to his “journey” (NIV) from Babylon to Jerusalem using this word (Ezra 7:9; cf. 2:1), so one interpretation is that this term recalls the return of the captives from exile in Babylon.
Perhaps the most common view is that pilgrims on their journey to Jerusalem for one of the three annual feasts sang these songs in anticipation of the festivities (Ex. 23-14-17; 34:18-24; Lev. 23:4-44; Deut. 16:1-7). The imagery of Psalm 126:5-6; 127:2; 128:2; 129:6-8; and 132:15 may allude to agricultural harvests.
The word translated “ascents” can also mean “steps” (used by Ezekiel to refer to the temple staircase, Ezek. 40:21, 31). Later Jewish tradition suggests that these fifteen songs were sung by Levites at the Feast of Tabernacles as they stood on each of the fifteen steps leading to the main court of the second temple. This latter interpretation does not exclude a possible earlier use of these songs during pilgrimages to the annual feasts.
Assuming that these psalms were used in conjunction with the great pilgrim feasts, they express a strong longing in anticipation of worship in Jerusalem.
–“Pilgrim Psalms” in Psalms: Zondervan Illustrated Bible
Backgrounds Commentary, John Hilber