I would say "web application backend". It's easy to instantiate a web server with a few lines of code. There is good library and open source support for things like database drivers, JSON, YAML, cache management, HTTP, gRPC. Goroutines allow for concurrency (e.g. processing many concurrent HTTP requests) with relatively low overhead.

EDIT: In terms of strengths it's a relatively small/simple language. Good out of the box tooling, e.g. profiling, linting, doc generation, package management, code formatting. Fast compile times. Garbage collected so not a lot of memory management headaches. Strongly types. Performant. (maybe not as easy to squeeze the last cycle out of things as you can with C or C++ but not an unreasonable tradeoff between performance and language runtime/abstractions).