SHELL

mongodb find like

db.users.find({"name": /.*m.*/});

db.users.find({"name": /m/});

Items.find({"description": {$regex: ".*" + variable + ".*"}}).fetch();

mongodb recherche like

db.users.find({"name": /m/})
or
db.users.find({"name": /.*m.*/})

You're looking for something that contains "m" somewhere
(SQL's '%' operator is equivalent to Regexp's '.*'), 
not something that has "m" anchored to the beginning of the string.