With thanks to the Solid works blog
The two main difference are updates and Support:
When you buy software with a licence, your licence never expires and you can use it forever. However, that doesn't give you the right to any new updates to the software. If you licence is a couple of years old and you want the new updates, you have to renew (pay) for a new licence.
Under a subscription model "you receive software updates automatically, so you have the latest and greatest version as soon as new functionality is ready and released. As the software becomes more efficient, you become more efficient too!"
In both cases, access to new features are generally excluded. Licence holders have to buy licences for new features and subscribers need to subscribe to new features when they are released.
Under a licence, you generally get 1 year support and then you have to pay for support after that.
With a subscription, support is automatically included.