For the visa waiver that is valid for 180 days and entitles its holder to spend up to 90 days in Qatar, does this mean that the holder cannot stay for more than 90 consecutive days during the 180-d...

Holders of the visa waiver that is valid for 180 days from the date of issue may not spend more than 90 days in total in Qatar during the 180-day validity period. For example, they can stay in Qatar for 60 days, leave, and return for 30 days, with a period of 180 days. With that they will have used up the total number of days they can stay in Qatar on this visa waiver.