Refers to the number of bits that can be processed or transmitted in parallel, or the
number of bits used for single element in a
data format. The term is often applied to the
following:
microprocessor: indicates the width of the
registers. A 16-bit microprocessor can process
data and memory addresses that are represented
by 16 bits.
bus : indicates the number of wires in the bus.
A 16-bit bus transmits 16 bits in parallel.
graphics device, such as a scanner or digital
camera : specifies the number of bits used to
represent each pixel.
operating system: refers primarily to the number
of bits used to represent memory addresses.
Windows 3.x is a 16-bit operating system,
whereas Windows 95 and Windows NT are 32-bit
operating systems.
expansion board: refers to how much data can be
sent to and from the card in parallel. 8-bit
cards are sometimes called half-size cards
whereas 16-bit cards are referred to as full-
size cards.
source: https://www.webopedia.com/TERM/1/16_bit.html