Usually, we refer to Typography as the art and technique of arranging type to make written language legible, readable, and appealing. Another definition by Gerrit Noordzji, he defines typography as “writing with prefabricated characters.

Lettering being defined as “art of drawing/ illustrating letter, words, and phrases.”

So when we talk about work like AIGA poster by Stefan Sagmeister what term would be the most suitable one to define it? Typography or Lettering?

5 hours ago, Niteesh said:

work like AIGA poster by Stefan Sagmeister what term would be the most suitable one to define it? Typography or Lettering?

Graphic designs, or simply graphics.

If you want a clever term, that is good for both the layman and the connoisseur, you can use typo-graphics.

5 hours ago, Niteesh said:

Usually, we refer to Typography as the art and technique of arranging type to make written language legible, readable, and appealing. Another definition by Gerrit Noordzji, he defines typography as “writing with prefabricated characters.

Both are basically the same, because “type” and “prefabricated characters” are the same thing. The first definition puts more focus on the art and purpose, the second on the technique. That’s all perfectly valid and common. 

 

5 hours ago, Niteesh said:

Lettering being defined as “art of drawing/ illustrating letter, words, and phrases.”

So when we talk about work like AIGA poster by Stefan Sagmeister what term would be the most suitable one to define it? Typography or Lettering?

In a strict sense, it’s definitely not typography. There are not fonts (“prefabricated letters”) used. 
Colloquially, typography is now often used in a much broader sense, but it’s usually frowned upon within the field of graphic design.