How is the term 'sessile' best defined?

The term 'sessile' is best defined as being permanently attached to something. This refers to organisms that do not move from one place to another and instead remain fixed in one location throughout their lives. Examples of sessile organisms include barnacles, corals, and many types of plants such as trees and certain algae. Being sessile does not imply the ability to move freely or swim, nor does it necessarily relate to the capability of photosynthesis, even though some sessile organisms like plants do perform photosynthesis. Thus, the definition focusing on permanent attachment is the most accurate representation of what 'sessile' means in biological contexts.