Parallel complexity theory is a subfield of computational complexity theory that investigates the resources required to solve computational problems using multiple processors working simultaneously. It focuses on determining the minimum time necessary to solve a problem given a sufficient number of processors and characterizes the class of problems efficiently solvable in parallel, often contrasting this with problems inherently sequential in nature. This field is significant for understanding the fundamental limits and potential speedups of parallel computation and informs the design of efficient algorithms for parallel computing architectures.