Complexity, in general usage, tends to be used to characterize something with many parts in intricate arrangement.
Following this disambiguation, and assuming that “many” means N > 2, all systems with at least two or more components are complex. But that would be an exaggeration, right?
Why is information technology complex?
Most systems in information technology (IT) are complex. Almost everything we are working with, consists of two or more components, regardless if it is hardware or software. But it’s a question of the perspective. If you look at a system from a higher level, you will only be able to identify some of the greater components. If you look closer at it, you will be able to identify more, smaller components. Every system consists of hardware and software. Hardware is nothing without software. Think of a storage system, with all those disks, controllers, disk enclosures, firmware etc. Or think bigger: A complete infrastructure based on a VMware vSphere cluster with multiple servers, network switches, SAN switches, storage systems, synchronous mirroring between data centers etc. The system can be split into its components and sub-components. And each component and sub-component is more or less important of the operational function of the whole system. Adding more features makes a system even more complex. With each added feature or modified feature, the probability rises, that something breaks or doesn’t work as expected.