Processes or tasks which run on a computer require various resources like CPU cycles, memory, disk or network which are managed by the operating system, so that each task executes efficiently (without waiting for a resource if possible).
OS tries to maximize resource utilization by letting many processes
use resources simultaneously. If a process requests a particular
resource in large amount, it can bottleneck (delay) its execution. The
process is said to be resource-intensive w.r.to that resource. So
resource-intensive is a relative terminology.
Sorting, search, graph traversal, matrix multiply are all CPU operations, a process is CPU-intensive or not it depends on how much and how frequent are their execution. For instance trans-coding video or compressing files is pretty CPU intensive, because they run the CPU operations far more than they need to read/write memory or disk. If you are planing on doing these, you should create a separate child process for it, so that it won't slowdown node process, which is single-threaded, or better create a node cluster.
