Stakeholders are all the people that are somehow involved with the product. Those can be your customers, the users of your system, or the management. Communication is a key skill for every architect and properly managing your stakeholder's needs is key to delivering what they expected and in a way they wanted.
Different things are important to different groups of stakeholders, so try to gather input from all those groups.
Your customers will probably care about the cost of writing and running the software, the functionality it delivers, its lifetime, time to market, and the quality of your solution.
The users of your system can be divided into two groups: end users and administrators. The first ones usually care about things such as the usability, user experience, and performance of the software. For the latter, more important aspects are user management, system configuration, security, backups, and recovery.
Finally, things that could matter for stakeholders working in management are keeping the development costs low, achieving business goals, being on track with the development schedule, and maintaining product quality.
