Fusional languages are a type of language where a single affix (prefix or suffix) can express multiple grammatical categories, such as tense, mood, and number. This means that a single word can convey a lot of information through its structure. For example, in Spanish, the verb form can change to indicate who is performing the action and when it is happening, all within one word. These languages often have complex inflectional systems, making them different from isolating languages, which use separate words for each grammatical function. Russian and Latin are other examples of fusional languages, showcasing how rich and intricate their grammatical structures can be.