Final answer:
A lava vesicle is a small hole formed in solidifying lava when trapped gas cannot escape. These vesicles are common in basaltic lava that flows quickly and hardens into rock. The term represents the void left by the gas upon the lava cooling.
Step-by-step explanation:
A lava vesicle is a small hole which develops in cooling lava when gas is unable to escape as the lava solidifies. When the lava from a volcano hardens into rock, gases that were trapped in the molten rock form these vesicles. The basaltic lava, known for its ability to flow quickly over long distances, often contains these vesicles which are created when gaseous effusion occurs as the lava cools and solidifies.