What does the "static" modifier after "import" mean?

There is no difference between those two imports you state. You can, however, use the static import to allow unqualified access to static members of other classes. Where I used to have to do this:

import org.apache.commons.lang.StringUtils;
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if (StringUtils.isBlank(aString)) {
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I can do this:

import static org.apache.commons.lang.StringUtils.isBlank;
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if (isBlank(aString)) {
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You can see more in the documentation.

See Documentation

The static import declaration is analogous to the normal import declaration. Where the normal import declaration imports classes from packages, allowing them to be used without package qualification, the static import declaration imports static members from classes, allowing them to be used without class qualification.

So when should you use static import? Very sparingly! Only use it when you'd otherwise be tempted to declare local copies of constants, or to abuse inheritance (the Constant Interface Antipattern). In other words, use it when you require frequent access to static members from one or two classes. If you overuse the static import feature, it can make your program unreadable and unmaintainable, polluting its namespace with all the static members you import. Readers of your code (including you, a few months after you wrote it) will not know which class a static member comes from. Importing all of the static members from a class can be particularly harmful to readability; if you need only one or two members, import them individually. Used appropriately, static import can make your program more readable, by removing the boilerplate of repetition of class names.