Multicellularity refers to the condition of an organism being composed of multiple cells that work together to perform various functions. Unlike unicellular organisms, which consist of a single cell, multicellular organisms can develop specialized cells that take on specific roles, such as muscle cells for movement or nerve cells for communication. This specialization allows for greater complexity and efficiency in biological processes. The evolution of multicellularity is believed to have occurred independently in different groups, including plants, animals, and fungi. This transition enabled organisms to grow larger, adapt to diverse environments, and develop intricate systems for reproduction, metabolism, and response to stimuli.