20. A computerized system facilitating a search, comprising: a fixed phrase detector configured to, at least: cluster keywords of previous searches into a plurality of keyword clusters; and detect at least one fixed phrase at least in part by identifying at least one search phrase comprising keywords of a distinguished cluster of the keyword clusters as having a relative high pointwise mutual information score with respect to counts of search phrases comprising keywords of the distinguished cluster; an index maintenance module configured at least to update a search index comprising a relevance score of each of a plurality of keywords and said at least one fixed phrase for at least some of a collection of content; a search module configured at least to provide at least one result of the search for presentation based at least in part on the search index; and one or more hardware processors collectively facilitating at least the fixed phrase detector, the index maintenance module and the search module.
20. A computerized system facilitating a search, comprising: a fixed phrase detector configured to, at least: cluster keywords of previous searches into a plurality of keyword clusters; and detect at least one fixed phrase at least in part by identifying at least one search phrase comprising keywords of a distinguished cluster of the keyword clusters as having a relative high pointwise mutual information score with respect to counts of search phrases comprising keywords of the distinguished cluster; an index maintenance module configured at least to update a search index comprising a relevance score of each of a plurality of keywords and said at least one fixed phrase for at least some of a collection of content; a search module configured at least to provide at least one result of the search for presentation based at least in part on the search index; and one or more hardware processors collectively facilitating at least the fixed phrase detector, the index maintenance module and the search module. 21. A computerized system according to claim 20 , wherein at least some of the plurality of keyword clusters correspond to unsupervised topics defined at least in part by a latent Dirichlet allocation.