It is a diminutive plural form of saying hello. Usually in Lthuanian we say "Sveiki".
For singular masculine form it would be "Sveikas"; deminutive - "Sveikutis";
For singular feminine form it would be "Sveikutė".
For plural feminine form it would be "Sveikutės".
For plural masculine or masculine+feminine form it would be "Sveikučiai".

So it can be translated as:
"Hello" or simply "Hi".

The explanation given for the grammar (plural dimunitive form) is correct and thorough. "Sveiki" would be hello or hi. The use of the dimunitive makes it more folksy. Thus, my suggestion.