Refers to a business that arranges travel, tours, and accommodations. Often used interchangeably with 旅行会社, though 旅行社 may sound slightly more formal or established.
See also: 旅行会社
I asked the travel agency to arrange next month's trip.
That travel agency has a great selection of overseas tours.
I booked a tour through a travel agency.
I asked the travel agency to arrange the flight tickets.