The DfE state: 

A Trust Partnership is a time-limited arrangement, allowing schools to partner with an academy trust. It does not deliver the full benefits of joining an academy trust but is a time-limited way for a school to benefit from trialling membership in an academy trust and explore how a permanent arrangement might work. This guidance provides information, case studies and model SLA to support academy trusts and schools to establish Trust Partnerships.

Full details are available here.