Emotive language is language meant to evoke an emotion. Examples include sentences that add extra adjectives to enhance the content, such as using the word "murder" instead of "capital punishment." Emotive language is common in literary fiction and poetry.
Emotive language is also used in persuasive writing to attempt to get the reader on the side of the writer. Most fiction uses emotive language so that the reader better feels what the characters feel and is more connected to the events of the story. A book that uses purely objective language is more difficult to rea, and getting in touch with the characters is hard and takes more work from the reader.
The same sentence can be read different ways depending on which type of emotive language is being used. For example, if someone puts down an animal it implies mercy and compassion, while using a word like "obliterate" lends the action a more violent, menacing feeling. Emotive writing can be overdone, taking away the freedom of the reader to come to his own conclusions about something; in fiction, emotive language is required to some extent. In non-fiction, emotive writing is best avoided except for persuasive writing, and even then it should be limited when possible.