Leaf query clauses look for a particular value in a field
Compound query clauses wrap other leaf or compound queries
behaviour of a query clause depends on if it used in query context or filter context
Query context describes "How well does this document match this query clause"
- bool decides whether or not it should match
- then assigns a _score representing how well the document matches, relatively
in Filter context, a query clause describes "does this document match this query clause?"

Relevance is the score of each document, represented by a positive float called _score

calculated depending on the type of query clause
a fuzzy query might determine the _score by calculating how similar the spelling of the found word is
algorithm known as term frequency/inverse document frequency, TF/IDF
- Term Frequency is how often the term appears in a field
- Inverse document frequency, how often does each term appear in the index, more often, the less relevant
  - common terms have lower weight
- Field-length norm, how long is the field, the longer the less likely a word in the field will be relevant