What is a unit in science?

Answer 1

A unit is an agreed amount of whatever is being measured. We all agree to compare something to the same thing. For instance, you could measure the length of a room by how many of your feet would fit it. If I do the same thing with my feet we'd get a different answer, so we all have to agree whose feet to use. That would be a standard foot. Most units evolved gradually like this, and their precise definitions have changed as people found new ways to be more accurate.

So, we can measure length in units of feet, inches and miles, or in grams and kilograms, but if you don't say what you're using any number you give is meaningless, so ALWAYS WRITE THE UNIT.