Shaping is the implementation of protocol-based priority, to manage demand on the network (i.e. some parts of the internet are made to be faster than others, using prioritisation).
When shaping is implemented, realtime, interactive services are given higher priority than non‑realtime, non-interactive services, effectively slowing the performance of non-prioritised services in favour of those that are more important to an overall good broadband experience. Shaping can be applied to any user on a shaped data package in general (not based on usage thresholds), and the impact to non-priority services is determined by the level of demand and available network capacity.
Shaping is applied only when demand on the network exceeds available network capacity, and relieved when demand decreases.