"Pipe" vs "tube" vs "hose"

If you buy a half-inch garden hose, the inside diameter is half-inch.

From Measuring Pipes and Pipe Fittings (PDF © Copyright 2011, Sears Brands, LLC., 6 pages) by Larry Johnston:

Pipe goes by nominal sizes rather than actual measurements, so identifying pipe size can be tricky. Copper 3/4-inch pipe, for instance, doesn’t measure 3/4-inch anywhere — its outside diameter (OD) is 0.875 inch and inner diameter (ID) is 0.811 inch for Type M pipe (a designation relating to wall thickness). But steel 3/4-inch pipe is 1.050 inch OD and 0.824 inch ID for standard Schedule 40 pipe (also a wall thickness designation). Plastic pipe measures the same as steel pipe.

To make things a little more confusing, sizes for tubing, such as the small-diameter plastic or copper tubing used to hook up icemakers, are the actual outside diameter and hose sizes indicate actual inside diameter.

Pipe, tube, and hoses. Hoses (including garden hoses) are measured by the ID. Tube is measured by the OD. Pipe is not measured: it's nominal.

It's less confusing if you know these details.

It's more confusing when the words "pipe" and "tube" and "hose" are used interchangeably.