The word “Rahao” (ਰਹਾਉ) in Gurmukhi means “pause.” Rahao is derived from “Raha” which means “to cause to remain, fix, support, restrain.” The Rahao appears frequently, in almost every Shabad contained within the Siri Guru Granth Sahib, the living Guru of the Sikhs.
The word Rahao always appears at the end of a line of Gurbani, which in Gurmukhi is called a “Tuk.” When used within Gurbani, Rahao literally means to pause in hymns when reading, and when singing, to repeat that line.
The line containing the Rahao contains the central idea of the Shabad. With the Rahao, the Guru is instructing us to wait or pause, and contemplate the preceding line or Tuk before proceeding. This is because the line with Rahao at the end captures the main theme of the whole Shabad.
This is the line in which the Guru is conveying the overarching topic discussed in the Shabad, and it thus contains the Gurmat Vichar, or the “right thought.” Therefore, Sikhs are required to pause on this line and contemplate the message.
The other lines in the Shabad are used to explain or further extrapolate on the central theme given in the line with Rahao. These other lines (the non-Rahao lines) generally talk about prevalent practices, arguments, reasoning, intention, etc., and are used for strengthening or explaining the central theme.
In the Siri Guru Granth Sahib, the numbering of lines is meaningful and intentional, and conveys a definitive message. When we encounter the Rahao when reading from the Guru, it will benefit us to read and re-read that line carefully, and allow this concept to fully permeate our consciousness before continuing. When reading the non-Rahao lines, we can contemplate how these correlate with the main message in the line with the Rahao.
Occasionally, more than one Rahao may be contained within a Shabad. If this is the case, they will generally both share the same central theme. It simply indicates that the Guru is conveying the same central theme in a different combination of words.
~Resource: Angad Singh, “Rahao” (SikhiWiki).