The discriminant tells us there are two roots when positive, one root when zero, and no roots when negative. b^2-4ac = (-8)^2-4*3*1 = 52 is positive, so there are two roots. The discriminant is just part of the quadratic equation. The quadratic equation gives us the exact real number roots of any equation in the form ax^2+bx+c=0. The quadratic equation is x = (-b \pm sqrt(b^2-4ac))/(2a), where \pm means that we have two values, one using + (addition) and one using - (subtraction). Let D = b^2-4ac.
A data warehouse is a special type of database used for analysis of data. A general database is usually used for transaction processing, and hence, it is not optimized for analysis and reporting. But a data warehouse is specially designed and optimized for analysis tasks.
Different vendors use these terminologies to mean different things. In Oracle-speak, a database is the collection of datafiles on disk. These datafiles belong to your tablespaces. They are also the online redo log files, the parameter file, the password file, and the control files. A database exists on disk and will be there even if you shut down the server and reboot it. But a database is not accessible by itself. You have to sign on to SQL*Plus and issue a STARTUP command.