elasticsearch what is the difference between best_field and most_field

Whenever search operation is performed in Elastic Search, relevance of each matched document is calculated.According to th documentation-

The relevance score of each document is represented by a positive floating-point number called the _score. The higher the _score, the more relevant the document.

As per your examples mentioned above

GET blablabla/_search{"query": {"multi_match": {  "query": "games usa",  "fields": ["title1", "title2"],  "type": "best_fields"   }  }}

This query will find the documents which contain games AND/OR usa in title1 or title2 but _score will be calculated from single best matching field. For example-

• if title1 contains games and title2 contains games usa in the same document, then _score will be the one from title2.
• best_fields is most useful when you are searching for multiple words best found in the same field.

In most_fields:

GET blablabla/_search{ "query" : {"multi_match": {  "query": "games usa",  "fields": ["title1", "title2"],  "type": "most_fields"   }  }}

This query will find the documents which contain games AND/OR usa in title1 or title2 but _score will be calculated from the combination of all the fields. For example-

• if title1 contains games and title2 contains games usa in the same document, then _score will be combination of scores from title1 and title2

Hope this helps

A little remark for most_fields - it uses score from both fields. and divide it on fields count

In your example:( Score from title1 + score from title2 ) / 2