The sidecar pattern is a design approach where a small service runs alongside the main application to handle operational tasks like logging, monitoring, and security. Similar to a motorcycle sidecar, it decouples these concerns from the core business logic. The pattern enables consistent infrastructure features across microservices, supports language independence, and allows updates without affecting the main application. However, it introduces resource overhead, latency, and operational complexity. Common implementations include Envoy for traffic proxying, Fluentd for logging, and Vault Agent for security management.