In a linear sequence, what exactly is the common difference?

1. A linear sequence steps up or down by the same amount every time. 2. The common difference is the difference between any two consecutive terms. 3. It is found by subtracting a term from the term that follows it. 4. Subtracting in the wrong order gives the right size but the wrong sign. 5. If the difference is not the same for every pair, the sequence is not linear. _Source: Siyavula Mathematics Grade 11 (Everything Maths, CC BY 4.0), Chapter 3: Number patterns_