According to the SAFe 6 Scrum Master documentation, the type of work that should fit into one

Iteration for one team is a Story. A Story is a short description of a small piece of functionality that

provides value to the customer or stakeholder. Stories are derived from Features, which are larger

units of value that typically span multiple Iterations. Stories are also decomposed into Tasks, which

are the specific activities that the team members perform to implement the Story. Stories are the

primary backlog items that the team plans, estimates, and delivers in an Iteration. They are also the

basis for defining and committing to the Iteration goals. Stories should be small enough to be

completed within one Iteration, and they should meet the definition of ready and the definition of

done. (Must be taken from SAFe 6 Scrum Master resources)

Reference:

Stories

Features

Tasks

Iteration Planning