Hello,
A hose is a flexible hollow tube designed to carry fluids from one location to another. Hoses are also sometimes called pipes.
With hydraulic hose assemblies, correct size depends upon ID (inner diameter), OD (outer diameter), and length.

Inner diameter is the bore of the hose and the size of the orifice that the fluid has to travel through over a particular length. The OD of the hose could be critical for various things like where the hose is going to fit and how strong the hose is. A very strong high-pressure hose tends to have a larger thickness as a ratio to its ID. And of course, the length will help you determine what kind of flow rates you can handle, factored in with your ID. Obviously a smaller hose will have a higher pressure drop or an overall long length than will a larger diameter hose.

I hope I have answered your query as expected.