ADS  (Alternate Distribution System)     
Used as a synonym for distribution via 3rd party Web sites, whereas we usually speak about the hotel distribution via online travel agencies. (also see IDS), such as Expedia and Travelocity 

ADR  (Average Daily Rate)           
Macro measurement used to calculate the average revenue achieved on consumed room nights  for a given period (day, month to date, month, year to date), divided by the number of rooms occupied for the same period. Frequently used as a measure of economic performance.

ADR  (Rate) Index
The ADR Index measures a hotel’s ADR performance relative to an aggregated grouping of hotels, competitive set, An ADR Index of 100 equals fair share of ADR, compared to the aggregated group of hotels. An ADR Index greater than 100 represents more than a fair share of the aggregated group’s ADR performance. Conversely, an ADR Index below 100 reflects less than a fair share of the aggregated group’s ADR performance. 

To calculate an ADR Index:
(Hotel ADR / Aggregated group of hotels’ ADR) x 100 = ADR Index
 For example, if the subject hotel’s ADR is $50 and the ADR of its competitive set is $50, the subject hotel’s index would total 100. If the subject hotel’s ADR totaled $60, its index would be 120, indicating the hotel has captured more than its fair share. If the subject hotel’s ADR totaled $40, its index would be 80, indicating the hotel has captured less than its fair share.

AIM  (Amadeus Instant Marketing)         
An Amadeus travel agent media product.  Amadeus Instant Marketing has the following products: Sign In Messages, Display Messages, Weather Messages and Broadcast Messages. This extensive line of media products provides travel suppliers with a wide range of options to get the right message, to the right audience, at the right time.

 ALOS  (Average Length of Stay)     
It is the total room nights booked where it can be segregated by segments divided by the total number of booked / reserved rooms for the hotel or for each segments.

The ALOS used to estimate the relative values of various segments and to keep tracking the hotel performance thus keeping guest in the hotel for long stays.

The calculation formula is by  dividing the total numbers of  occupied nights by / total booking made

 AP  (American plan)        
Also known as 'full pension' or Full Board , this describes a type of hotel plan or room rate which includes the price of three meals "breakfast, lunch, and dinner" daily added to the room rate

 AR  (Accounts Receivable)        
Direct bill accounts of companies or individuals who buy hotel services.

 ARI  (Average Rate Index)           
Percentage of calculating the ratio between the Total average room rate in a hotel against the Total average room rate generated by the comp set  collectively attributed to the hotel’s Market Set. 

 ARR  (Average Room Rate)          
See ADR

A la Carte Menu       
A menu of food and drinks in which each item is individually listed and priced.

 Actual Share 
The actual percentage of the room nights or revenue (based upon competitive set) that a hotel captures during a particular time frame.  Calculated by dividing the total room nights or revenue sold at the hotel by the total room nights or revenue sold within the competitive set inclusive of the subject hotel.

 Ad Impression, Ad Request, Ad Views     
The request of an advertising element as a direct result of a visitor’s action, as recorded by the advertisement server software.  An ad request does not guarantee that a visitor actually viewed an ad; it only measures the opportunity for an ad to have been delivered to the visitor.  This means that an ad request will be considered valid regardless of the visitor'’ ability to view graphics, and whether or not the HTML document containing the ad loads to completion.

 Ad Units        
A means of classifying ad types. For example, Internet ad units can include banners, buttons, daughter windows, pop-ups, interstitials, tag lines, etc.

Adjustments
A correction or modification to an existing checked-out reservation to reflect actual conditions

 All Inclusive  
Includes: 3 meals, snacks, drinks, kids' programs, and the use of other specified facilities.

 Amadeus       
A worldwide GDS based in Europe.  Principal partners are Air France, Lufthansa German Airlines and Iberian Airlines

 Apollo            
Originally developed as the internal CRS for United Airlines.   Apollo is the GDS operated by Galileo International from offices in Rosemont, Illinois.  Marketed in Canada, Europe, South America, Asia, and Africa under the Galileo name and in the United States and Mexico as Apollo

 Available Room Nights       
The total number of room nights that can be sold (often referred to as inventory).

 Availabl Rooms (suites, beds)     
The number of rooms available to guests for occupancy on a day-to-day basis, besides those available permanently for some use other than guest occupancy.

 AXESS          
GDS developed by Japan Airlines to serve primarily Japanese travel agents and travel planners