Serial/Parallel have commonly accepted technical meanings in the context of data interfaces which aren't necessarily intuitive.
Parallel refers to taking a raw bit stream and sending N bits at a time down N wires to a receiver who reads N bits at a time and reconstructs the bitstream. This was a common technique in the early days of computing because it is very simple to implement and low clock speeds meant it was often the only practical way of increasing the throughput of an interface.
As clock speeds increased, keeping each of the N signals in sync became increasingly difficult. This eventually lead to parallel interfaces falling out of favor and serial interfaces becoming dominant.
The defining characteristic of a serial interface is that the data signal itself also serves as the clock signal which keeps sender and receiver in sync.
Modern "parallel serial" interfaces like USB 3 consist of multiple serial links which are multiplexed using a framing protocol of some sort. So from a signaling standpoint they are still considered serial interfaces, even though data is in fact being sent in parallel.
Parallel refers to taking a raw bit stream and sending N bits at a time down N wires to a receiver who reads N bits at a time and reconstructs the bitstream. This was a common technique in the early days of computing because it is very simple to implement and low clock speeds meant it was often the only practical way of increasing the throughput of an interface.
As clock speeds increased, keeping each of the N signals in sync became increasingly difficult. This eventually lead to parallel interfaces falling out of favor and serial interfaces becoming dominant.
The defining characteristic of a serial interface is that the data signal itself also serves as the clock signal which keeps sender and receiver in sync.
Modern "parallel serial" interfaces like USB 3 consist of multiple serial links which are multiplexed using a framing protocol of some sort. So from a signaling standpoint they are still considered serial interfaces, even though data is in fact being sent in parallel.