axis1

Axis1 is a term used in mathematics and computing to denote the first non-scalar dimension in a multi-dimensional array or tensor, commonly referred to as axis 1. In many programming contexts, axes are zero-indexed, so axis 1 is the second dimension.

In the context of two-dimensional arrays, axis 0 typically represents the rows, while axis 1 represents the columns. Operations that reduce data along an axis, such as sum or mean, apply to that specific dimension. For example, in a 2D matrix with shape (m, n), reducing along axis 1 yields a result with shape (m,).

In higher dimensions, axis 1 remains the second dimension, though its interpretation depends on the data layout. In image data, for instance, different frameworks use different conventions for axis order (such as channel-first or channel-last), which affects what axis 1 represents. In many common libraries, axis 1 is simply the second coordinate axis of the tensor.

Usage notes: axis indices are often configurable and may be negative to count from the last axis (for example, axis -1 refers to the last dimension). While axis1 is sometimes used informally to refer to axis 1 in code or documentation, most libraries specify axis by a numeric index (such as axis=1). Different tools may also adopt subtle differences in axis semantics, particularly for Pandas, NumPy, and deep-learning frameworks.