Tenant isolation in multi-tenant systems is crucial for ensuring secure, separate access for every user. It's like a big apartment building where different families (or tenants) live, each with their own locked door and private space. Each tenant can only see and use its own things, just like each family has its own apartment. Tenant isolation comes in different levels, including fully isolated, fully shared, or something in between. Data isolation is achieved through various methods such as shared databases, separate schemas, or separate databases. Encryption plays a critical role in securing data at rest and in transit. Resource isolation ensures that computational, storage, and network resources assigned to one tenant are isolated from those of other tenants. Network isolation involves creating logical and/or physical boundaries between tenants' network traffic to prevent unauthorized access. Authentication and authorization mechanisms ensure users only access their own tenant's data. Tenant context is added to every request to keep track of which tenant a user belongs to, while compliance and legal isolation refer to ensuring that each tenant's data remains legally separate from others in a way that respects the privacy, security, and compliance requirements specific to each tenant.