If I use a bridge to perform traffic sniffing like man in the middle will the bridge add a delay? And what word should I use delay or latency?
Hi and welcome to Network Engineering.
As for "delay" vs "latency": The terms are not always used consistently. Some hints may be found here.
I think generally, the term latency is used when looking at end-to-end times for one direction, which essentially are composed of the sum of all propagation, serialization, buffering (and possibly processing) delays introduced by the various components along the path from source to destination (and back, if one wants to talk about round trip times (RTT) ). So you may say that a bridge adds some delay to the overall latency.
(next section edited after a helpful comment) A bridge, when compared to a direct cable, will add at least once the serialization delay of the given network medium (of the bridge's egress side), after processing it, to send the frame's bits out again on the egress side. Of course, one amount of serialization delay is added per direction, and since the majority of use cases requires (at least some) data to flow in either direction, the bridge will eventually add serialization delay twice.
In your case, some additional buffering and processing delay will occur due to the "man in the middle thing". How much that will be is entirely up to the processing capacity of the given bridging software on the given platform, and the various features and modules the frame is being subjected to.
Yes, a bridge / switch adds some delay to a frame - in the order of 1 to 20 µs.
For switches you usually speak of latency - the delay between receiving a frame and forwarding it out another port. A switch requires some time to receive the destination address and make the forwarding decision. Store-and-forward switches (the common kind) need to receive the entire frame before starting to forward. High-speed cut-through switches can get below 1 µs. Edit: as @kasperd has correctly pointed out, cut-through is only possible with source and destination ports at the same speed or stepping down.