Dimensions is an appropriate term, though dimensions needn't be constants. The last two columns have a common header and two subheads. The first column, after the first two rows, contains the row headers. Some parts of a table may have 2 dimensions, others three, others four, etc. Dimensionality higher than 2 are projected onto 2 in a table presentation.
User agents provide users with header information and other contextual information.
Render cells as blocks. This may assist some screen readers. Using this strategy, the user agent might render individual cells with the relevant top and side headers attached. When the selection is on an individual cell, the user would be able to use a keyboard command to receive the top and left header information for that cell. The user agent should appropriately account for headers that span multiple cells.