dedicated bandwidth Vs shared bandwidth

Does dedicated BW mean that during the whole connection, the user will have the same BW available, no matter how many other users are active in network?

While shared BW means that the momentary available BW for a user depends on how many users are active in the network in each moment?

Thanks.

Yes, that's exactly what it means. Keep in mind technically speaking all bandwidth is shared on the Internet, the pipes are so big though you'll never notice.

Thanks.

Actually, I noticed that during certain parts of the day, download is more slowly than in other parts.

Could be your provider, could be your area of the net or it could be the specific site you're visiting, if it's a general all around slowdown to all sites it's probably your ISP. Depends on what kind of connection you have DSL cable or something else?