Linked Analysis refers to the connection of two or more charts/tables of the same data, such that a change to the representation (filter, drill) in one affects the representation in the other.
Linked Analysis is called "linked" not because of a model link on dimensions, but because it links a set of widgets (charts/tables/geo maps) where one or more widgets can be drivers and/or receivers of filtering/drilling operations. By default linked analysis can only be done with charts/tables/geo maps using the same model. For more details please have a look at the the wiki page about Linked Analysis.
Filtering Across Models
When filtering across models is enabled linked analysis can be performed with charts/tables/geo maps that use different models. To enable filtering across models a user has to set up a link between the models in the story "Linked Dimensions" dialog, which means that one defines which dimensions of one model link to which dimensions of the other model. For more details please have a look at the the wiki page about Filtering Across Models.
Blending refers to combining data from multiple models in one chart/table. For this the same linking of dimensions is used as for enabling filtering across models. For more details please have a look at the the wiki page about Blending.