Is it visual aid or aide?

Visual aid is the only correct spelling. It describes a visual instructional device (e.g., a diagram) to help others understand the information presented. It can also refer to a device that helps one to see, such as glasses or a magnifying glass.

Aid often follows an attributive noun or adjective (e.g., “visual”) to specify the type of help.

“Visual aide” is a common misspelling.