An Ethernet switch is the central element of a LAN network and operates at data link OSI layer.
Every switch port defines a collision domain and can extend a broadcast or broadcast frame domain that is stopped by a router routed interface that operates at network OSI layer.
By default switches support one broadcast domain that can be tight to the default VLAN. VLANs, Virtual LANs, allow extension of this number to no more than the reserved 12-bit coded in the IEEE 802.1q frame header. This number depends on other design and technology considerations: VTP deployment, reserved VLANs, etc.