In identifying an essential function to determine if an individual with a disability is qualified, the employer should focus on the purpose of the function and the result to be accomplished, rather than the manner in which the function presently is performed. An individual with a disability may be qualified to perform the function if an accommodation would enable this person to perform the job in a different way, and the accommodation does not impose an undue hardship. Although it may be essential that a function be performed, frequently it is not essential that it be performed in a particular way (EEOC, 1992).
The term ‘job description’ is a flexible one, but here I’ll be using it in a modern context, to describe all of the copy you’d use on an online job board. It usually includes information like job title, duties, salary, etc.