Legal terminology may often be confusing, and this becomes apparent when applied to traffic laws- the ones we most commonly run afoul of. Two terms that are often intermingled are DWI (Driving While Intoxicated) and DUI (Driving Under the Influence). In some states the two terms are both used to describe impaired or drunken driving: in others both terms are used, with DWI referring to driving while intoxicated specifically by alcohol and DUI being used when the driver is charged with being under the influence of other drugs. The drugs don't necessarily have to be illegal narcotics for a DUI to be issued - they can simply be over the counter medication or prescription drugs. In some states DUI is a lesser charge signifies a lower degree of intoxication (as determined by a person's blood alcohol level at the time of arrest). For example, New York differentiates between DWI and DUI by establishing a blood alcohol level of .08 as the legal limit for DWI. If a person has a blood alcohol level of .07, the charges may be reduced to a DUI which carries a lesser punishment.
The distinction for the federal government is also based on severity; A DWI is issued when the blood alcohol content (BAC) is over the 0.08 limit, whereas a DUI (a less severe term) applies when a persons BAC is under 0.08. Because individual states have the power to regulate their own DWI/DUI laws the specifics vary across the country.
In Texas, the distinction is relatively simple: DWI is defined in Sec. 49.04. of the Texas State Penal Code and applies to any person over 21 years of age. In Texas, a person is legally intoxicated and may be arrested and charged with Driving While Intoxicated (DWI) with a .08 BAC (blood or breath alcohol concentration). However, a person is also intoxicated if impaired due to alcohol or other drugs regardless of BAC.
Texas DUI specifically refers to minors (persons under the age of 21) who operate a motor vehicle in a public place while having any detectable amount of alcohol in their system. Generally, an offense under this section is a Class C Misdemeanor.