Stop-words are "filler" words that don’t provide much information to a sentence. Classic examples are words like "the", "and", "or", "but". It is common to remove stop-words in both structured and unstructured search.
Elasticsearch provides a Stop filter which can be configured to remove
words from the token stream. Stop-words can be provided in the mapping itself
as an array of terms, or it can be configured in an external file. If your
list of stop-words is large it is recommended to use the external file.
Importantly, stop-words in your list must match a token exactly to be removed. In almost all situations you should first lowercase the token stream before removing stop-words.
If you didn’t lowercase first, you may miss stop-words that have alternate case (e.g. "The" vs "the").
An example mapping which places a Stop filter after Lowercase:
"analysis":{
"analyzer":{
"default-analyzer":{
"type":"custom",
"tokenizer":"standard",
"filter":[ "lowercase", "my_stop_filter" ]
}
},
"filter":{
"my_stop_filter":{
"type":"stop",
"stopwords":[
"the", "a", "to", "but", "or", "and"
]
}
}
}