No, but yes.
JDK means Java Development Kit 6.
It’s an implementation of the Java SE 6 platform as specified by JSR 270 together with a set of development tools (the implementation of the platform without the development tools is called the JRE: Java Runtime Environment).
For some reason the internal version number of the JDK 6 is “1.6” (or 1.6.0_17 for example). But that’s only the internal version number of that piece of software. The Java platform itself is simple “Java SE 6” (no “1.” anywhere to see).
So to re-iterate:
- “Java 6” usually means “Java SE 6”
- “Java SE 6” is the “Java Standard Edition 6 platform”, which is a specification of what the platform looks like
- “JDK 6” is the “Java Development Kit 6”, which is a development kit for Java SE 6
- The internal version number of the software components that make up JDK 6 is “1.6.x”
- “JDK 1.6” doesn’t exist, strictly speaking, but is usually written to refer to JDK 6
- “Java 1.6” doesn’t exist, strictly speaking, but is usually written to refer to Java SE 6
So if you’re told to install “Java 1.6” for a software development course, then the JDK 6 is definitely the correct piece of software to install.
Update: yes, all of the above is still correct after Oracle bought Sun and Java 7 (specified in JSR 336) was released. Java 7 still uses “1.7.0” as the internal version number.