I am purchasing on behalf of an organization

[HaiMai]

As I know, ArcGIS Desktop has  single use and concurrent use. I don't understand the meaning of "I am purchasing on behalf of an organization". Does it imply the "concurrent use" ?

[DanPatterson_Retired]

Are you buying the software for your own use or are you buying it for a company.  If you are buying it for yourself is the only question.  With the important qualification...

ArcGIS for Personal Use is ideal for existing ArcGIS users who want the same powerful software at home for noncommercial, personal use.

In short... you can't use it to run a business or commercial enterprise of any kind.

[HaiMai]

I want to buy for a company

[DanPatterson_Retired]

Then the other option is for you and you just have to chose the license level, Basic, Standard or Advanced

https://www.esri.com/en-us/store/arcgis-desktop 

plus extensions etc.  The option information is on the site but you would be recommended to consult with your local representative for specific configurations etc.

[AlanaBaker3]

"I am purchasing on behalf of an organization" will link all the purchases to your Organization's account.  You have or will receive a customer number so you can keep track of all your purchases, licenses and users within the organization.  You still have the option to purchase Single Use on behalf of the Organization.  If you want more information, I would contact your local Esri office, as Dan suggested above.