A Dependency Parser extracts a dependency graph from a sentence. In the graph the grammatical structure is represented and relationships are defined between head-words and words, which modify these heads. For example, most sentences have a root-word, which is the main verb, a subject and an object. All tags are defined on the Universal Dependency Relations website. You can also play with the displaCy Dependency Visualizer demo.
Dependencies are also great for Information Extraction, because there often is an object-subject relation. Spacy is very useful for navigating the dependency parse tree as you can see in this example.
This article is part of the project Periodic Table of NLP Tasks. Click to read more about the making of the Periodic Table and the project to systemize NLP tasks.