Bandwidth
The maximum rate at which a link or path can carry data, stated in bits per second; a capacity figure, distinct from throughput, which is the rate actually achieved.
Bandwidth is the capacity of a communication channel: the maximum amount of data it can carry per unit of time, stated in bits per second and its multiples. The word comes from signal engineering, where it names the range of frequencies a channel occupies, measured in hertz; a wider range can carry more data. In networking it is used for capacity. The ISC2 exam outline lists it first among the Domain 4 performance metrics, beside latency, jitter, throughput and signal-to-noise ratio.
Bandwidth is not throughput. Bandwidth is what the link could carry; throughput is what actually gets through once protocol overhead, congestion, retransmissions and errors have taken their share. Latency is a separate property again: a high-bandwidth link can still respond slowly if the delay across it is long, as on a geostationary satellite path. For security, bandwidth matters mainly as an availability resource. A volumetric denial of service attack works by exhausting it, and quality of service and traffic shaping exist to divide it between competing traffic so that critical flows still get through.
Exam relevance: questions in this area tend to turn on keeping the metrics apart. Capacity is bandwidth, delivered rate is throughput, delay is latency, and variation in delay is jitter. Candidates are expected to link bandwidth exhaustion to availability rather than to confidentiality or integrity.