32-Bit refers to the number of bits that can be transmitted or processed in parallel. In other words, 32-bits is the number of bits that compose a data element.
For a data bus, 32-bit means the number of pathways available, meaning that it has 32 pathways in parallel for data to travel.
For microprocessors, it indicates the width of the registers and can process any data and use memory addresses that are represented in 32-bits. This is part of the processor’s architecture.
For operating systems, 32-bits refer to how it handles data. It is used to represent a memory address and works in conjunction with the microprocessor.
As for graphic devices like digital cameras or scanners, it refers to the number of bits used to represent the pixels. 24-bits are used for color information and 8-bits are used for the control information (alpha channel).