Backlog items.
Explanation:
The Sprint Backlog is the set of Product Backlog items selected for the Sprint, plus a plan for delivering the product Increment and realizing the Sprint Goal1. The Sprint Backlog is a forecast by the Developers about what functionality will be in the next Increment and the work needed to deliver that functionality into a "Done" Increment1. The Sprint Backlog makes visible all the work that the Developers identify as necessary to meet the Sprint Goal1. The Sprint Backlog can include any items that the Developers deem necessary to achieve the Sprint Goal, such as user stories, tasks, use cases, tests, or others. The Sprint Backlog is a plan with enough detail that changes in progress can be understood in the Daily Scrum1.
Reference:
The Scrum Guide, section 3.3. Sprint Backlog
Professional Scrum Product Owner I (PSPO I) Learning Path, section 2.2. The Product Owner and the Sprint Professional Scrum Product Owner I (PSPO I) Sample Questions, question 11

In accordance with Scrum theory, a group of 100 people should be divided into multiple Scrum Teams by understanding the product, the product vision and the rules of the Scrum framework, and then dividing themselves into teams because:
* It respects the self-organization and empowerment of the people. The people are the ones who have the knowledge, skills, and experience to create and deliver the product. They are also the ones who will work together as Scrum Teams, collaborating and coordinating their efforts. Therefore, they should have the autonomy and authority to decide how to form their teams, based on their preferences, interests, and capabilities.
* It supports the alignment and coherence of the Scrum Teams. The people should have a clear and shared understanding of the product, the product vision, and the rules of the Scrum framework before forming their teams. This can help them to align their goals and missions, to ensure that they are working on the same product and towards the same vision. It can also help them to follow the same principles and practices of Scrum, to ensure that they are working effectively and consistently.
* It fosters the collaboration and synergy of the Scrum Teams. The people should form their teams in a way that maximizes their collaboration and synergy. This can mean choosing team members that complement each other's skills and strengths, that have good rapport and trust, that can communicate and coordinate well, and that can deliver a valuable Increment each Sprint.
References:
Scrum Guide 2020, page 5: "Scrum Teams are cross-functional, meaning the members have all the skills necessary to create value in each Sprint." Scrum Guide 2020, page 5: "Scrum Teams are self-managing, meaning they internally decide who does what, when, and how." Scrum Guide 2020, page 9: "Multiple Scrum Teams working together on a product use one Product Backlog." Scrum Guide 2020, page 9: "The Product Owner is one person, not a committee."