Communities of Interest are clubs that may meet online or in-person. This is where people meet to share their experiences, ideas, knowledge, skills and wisdom. They are usually organized around a shared interest in a recreation, do-it-yourself (DIY), hobby or public issue. Its simple — people helping people with tips and hacks, etc.
Communities of Practice are usually more involved than communities of interest. They are organized around sharing best practices in an industry, discipline, occupation or profession. They tend to be more formal and business-like.