Is there anybody in world who know what's the difference between genre and style in music? In wikipedia there are articles: list of music genres and list of music styles, but when we will go to particular page of music style we will often see something like: "Name of musical style - is a musical genre ...".
These words are very dependent on the context, and in many cases, they can even be treated as synonyms. That's one reason why you see them being used interchangeably: in case there is no possible confusion, either word can be used.
One way to look at it
I am not completely sure if this is the correct way to look at it, but I've always seen it like this: genre is much more broad than a style. A style can be seen as a subdivision of a genre.
For instance, rock music is a genre. Alternative rock, progressive rock and orchestral rock are styles of rock music.
This is not completely set in stone though, so don't shoot somebody when they say progressive rock is a music genre. :-) You'll see the terms being used interchangeably quite often, simply because their meanings are so closely related.
Another way to look at it:
A "genre" is the word for a categorization, so rock music, progressive rock, etc are all genres. Think of a genre as a label.
A "style" is what you call a specific element of the music. For instance, David Gilmour's guitar playing style is melodic with lots of string bends.
For practical purposes, the two words are mostly interchangeable.
Style: sometimes people say "style" to refer more to the conventions of rhythm, harmony, melody, arrangement and production that might be associated with music of a particular type, from a particular area, or of a particular genre. Because of this you can hear people say things like, "I consider myself a contemporary electronic/dance artist, but I draw alot of my inspiration from the funk style of the 80's."
Genre: genre has a slightly more taxonomical meaning, in that it usually relates to an attempt to group music into somewhat arbitrary structurally related genres and sub genres. I say arbitrary because music is not science and any system of classifying must be at least partially subjective. For instance, at the highest level you might distinguish between instrumental and vocal music. Or between broad groups such as pop, rock, metal, world, concert/classical, jazz/blues/r&b, funk/motown. Each of these has quite a few sub genres. And there is a great deal of "overlap" and borrowing going on. There are heavy metal guitar players who play classical violin etudes, for example. But in the event of genre-crossing, the genre classification tends to be made on the basis of the audience it's aimed at. Although some metal fans may be open to hearing classical music on electric guitar, this kind of performance of classical repertoire is not often heard in the concert hall and so you might say that the average listener of classical music is somewhat uninterested in hearing this type of interpretation of classical music.
Genre means "type" or "category". It refers to broadly defining aspects shared by musical compositions, most often aspects of the music's instrumentation or its particular use, ethnicity etc. - e.g. popular, rock, punk rock; Latin-American music, samba, tango; jazz, trad jazz, bee-bop, improvisatory jazz; classical, orchestral, symphonic music, symphonic poem; concerto, violin-concerto; music for one performer; piano-music, piano-duet music; dance-music, ballet-music, waltz, nocturne, march; music for voice, opera, choral music, vocal-quartet music, Broadway musical, film-music ETC. ETC.
Style refers to characteristic features of how music (of a certain era, or within some particular genre) is played or expected to sound, i.e. its actual musical content - the set of expected musical patterns, mannerisms, expressive devices it conventionally makes use of. "Baroque", "Classical", denote differing styles that are recognizable by their own characteristic musical idioms. Jazz, while constituting a genre, also qualifies as a style (or group of more specific styles), since it makes use of particular performance idioms and techniques. "Sonata" similarly denotes both a genre and a particular style that is defined by an expected formal succession of events or architectural plan. "Free-style" implies a composition is not built on any predetermined architectural plan or incorporates a diversity of arbitrarily chosen stylistic idioms.