Is it just the frequency range that a particular wireless communication technology operates in? (for example WiFi 2.4 Ghz band (2,400 to 2,483.5 Mhz)). Can a frequency range of one technology overlap with another? If yes, what happens when they overlap? what differentiates one from another in that case?
They overlap a lot. Wifi and bluetooth and a number of bespoke wireless communication systems share the same frequency band... as does your microwave oven, for that matter.
It's the protocol that differentiates them, not anything to do with what frequency you run them at. You could theoretically use wifi at a completely different frequency, if you had a license to broadcast on that frequency. It just wouldn't be supported by anything else. (It wouldn't be standards-compliant wifi either as the 802.11 standard does specify frequency bands, but the protocol itself is independent of frequency as far as I know.)
Different wireless technologies can work in very different ways. Any technology can in theory be used in any frequency band. However two present in the same band will tend to interfere with each other's signals unless special precautions are taken.
For example WiFi, bluetooth, microwave ovens and car door keys all use 2.4 GHz. But if a badly maintained (dirty or damaged) microwave oven is on, it can leak enough RF power to disrupt WiFi and car locking. WiFi accepts this and if an oven is in the way it will change to a clearer frequency, while car owners just have to wait for the neighbour's oven to ding (been on both sides of that one!).
With digital technologies it is relatively easy to operate multiple channels on the same frequency band, provided you both agree what makes your signal special. For example WiFi and bluetooth devices are designed not to mistake each other's digital codes for their own.
On the other hand, for mobile phones and broadcast radio to interfere would be disastrous, so they are allocated strict frequency bands which they must stay within.
In the big picture, the two things that differentiate wireless communication strategies from each other are throughput and range. Within these, are power and cost.
Throughput is determined by channel bandwidth and by the modulation scheme used to encode the data. In the 2.4 GHz band, 802.11bgn supports 20 or 40 MHz channels, and using the modulations available with ‘n’, up to 300Mbit/s. This speed comes at a cost in both silicon and in power consumption, so it’s not the best choice for very small devices (yes, I know about the Roku wi-fi remote. It’s terrible.)
I’ll interject here that 802.11 has a wide range of protocols at its disposal, and will choose one appropriate to the signal strength it can see. This makes Wi-Fi even more complicated and expensive if it is to support ‘all the things’. That said, silicon being silicon, the overhead of this cost lessens all the time, to the point where we now see low-cost embedded SoCs with built in Wi-Fi like the ESP32.
Bluetooth on the other hand uses narrower channels than Wi-Fi, and employs simpler modulation schemes. Its typical baseline throughout is only 250kbps (even lower for BLE) and power levels typically 1/10 those of Wi-Fi. This makes it possible to use BT for in-ear headsets, remote controls and other low cost, space- and power-constrained devices that would otherwise not be feasible with Wi-fi.
Both BT and 802.11 are range limited - about 10m for Bluetooth and 30m for Wi-Fi in real-world use. Other protocols like LoRa and 802.15.4 have come about to address this, trading throughout for increased range by adopting only robust channel coding that can work with lower signal/noise ratio. More about those here: https://ieeexplore.ieee.org/ielx7/6287639/8948470/09181518.pdf
All these share the 2.4 GHz band at times, and so must be designed to coexist with each other. In reality it’s BT, LoRa and other low-bandwidth protocols that have to be agile to avoid 802.11, much in the same way small boats have to be maneuverable to avoid big ships even though they have the same right to use the water.