The word "凹槽" is formed by combining the character "凹", which means concave or sunken and is pictographic, depicting a depression, with the character "槽", which means groove or slot and is semantic-phonetic, indicating a trough or channel. Together, they create a compound word where "凹" describes the concave shape and "槽" specifies the type of indentation, resulting in a term that directly denotes a concave groove or recessed slot.