Regular Form refers to chains that a have a specific, repeatable structure, otherwise known as patterns. Typically, these chains move across the board rather than upwards. This is because chaining across the board uses space more efficiently and doesn't hinder you later on (unless you know what you're doing).
The two most common types of patterns are Stairs and Sandwich. If you're a beginner, you should make it a priority to learn these two patterns as soon and as well as possible.
A combination of both Stairs and Sandwich concepts.
Reversible Stairs and Sandwich
From one direction it's a Stairs chain, from the other direction it's a Sandwich chain.
A combination of both Stairs and Sandwich. This term gets thrown around a lot without people really knowing what it means. If you look closely, you'll understand.