Question

what is a sequence ?

Answer 1

A sequence definitely has more than one meaning depending on the field it is being used in. Generally sequence is used to depict a normal order of anything.

Anything that happens in a particular order and at regular intervals would be expressed using sequence.

Scientifically, sequence is also used to depict the chemical elements.

Answer 2

A sequence is just a set of things (usually numbers) that make a pattern.  

Or,

A list of numbers or objects in a special order.

• Example : 1, 2, 3, 4, 5… a sequence starting at 1 and increasing by 1 each time  

• Example: 3, 5, 7, 9,... is a sequence starting at 3 and increasing by 2 each time.
• Example: 5, 10, 20, 40, 80...  is a sequence starting at 5 and increasing by 2 times its preceding term each time