Software architecture refers to the organization of a system, a reflection as to how all systems work together.
Software architecture is like housing architecture.
When building a house, you first architect it. Each room is designed for a specific purpose.
Piping and electricity is diligently planned to interact throughout the house.
Doors allow you to travel between rooms whereas walls block off access to rooms.
Software architecture is the organizational makeup of the entire system.
Your software architecture is going to be the foundation of your product, so it is important that you understand this term, why it matters, and ensure that your developers are planning ahead to build a proper architecture. If you skip over on this step and don't plan ahead, you will create many problems for yourself as you scale.
This term is even more important once your product is live because with proper architecture comes proper scalability. As you want to build new features, integrate with other platforms, it is important that you do so in a way that aligns with scalable architecture.