According to terms of service of this site, can I create a account as my company name?
For example: assume that I have company / Business / Start-up called "ABCDEF".
Can I create a Stack Exchange account with "ABCDEF" as display name?
Barring any legal considerations and rights to use that name, you can use a company name as your user name/identity. See Usernames as advertising or spam.
But keep in mind that our Terms of Service require that accounts be owned used by an individual (i.e. not a corporate entity), so folks can not create a shared account for use by their "organization".
I've seen some companies doing this already, e.g. when they use Stack Overflow as part of their product support system.
From the Terms of Service, section 7:
As a condition to using Services, Subscriber may be required to register with Stack Exchange and select a password and profile name.
Subscriber may not (a) select or use as a profile name a name of another person with the intent to impersonate that person; or (b) use as a profile name a name subject to any rights of a person other than Subscriber without appropriate authorization.
(b) implies that if you do have the rights, it's no problem at all.
A related discussion can be found here.