The sound recorder is arguably the most important piece of location sound equipment in audio systems. Modern DSLR and mirrorless cameras deliver outstanding still and motion pictures, but seldom produce superior audio. Using a separate high-end sound recorder ensures your videos and images are accompanied by high-quality audio.
Portable recorders come in many forms, each with its own specific features. If you also shoot video, you'll need a unit with an integrated microphone for basic audio, or inputs for higher-quality mics.