Explain the concept of a slice's capacity and length in Go.

In Go, a slice has both length and capacity. The length represents the number of elements currently in the slice, while the capacity indicates the maximum number of elements it can hold without reallocating the underlying array. As elements are appended to a slice, its length increases. When the capacity is exceeded, a new larger array is allocated, and the slice's capacity is increased accordingly. Understanding these concepts is crucial for efficient memory management and preventing unnecessary reallocations.