You often hear the terms Subnet and VLAN used interchangeably.  With the ubiquitous nature of IP these days, when are the two not considered roughly the same from a high-level, understanding that VLANs are L2 and Subnets are L3.   In other words, are there any cases for having a VLAN without a Subnet, and still have IP (L3) communication?  [Also ignoring that all networks are not subnets when considering classful networks which all are really just CIDR prefixes these days.]
If they are used interchangeably then they are used incorrectly.

Subnet refers to particular IP network, such as 192.0.2.0/28.  

VLAN refers to 802.1Q standard, in which you can essentially give each port unique MAC address table, effectively separating them from each other.

VLAN may transport one or more subnet (but does not have to, it may be transporting something else than IP entirely). 
Subnet may be configured for VLAN, but does not have to be, it could be without 802.1Q or over some completely different L2 technology than ethernet.
