Used to describe objects that aren't strong or durable. Think of things that break easily. The flimsiness of the cardboard boxes made them unsuitable for shipping heavy items.
Pro Tip 2/3
Metaphorical Use
Can refer to abstract things, like plans or ideas, that lack substance or strength. His plan failed due to the flimsiness of the underlying concept.
Pro Tip 3/3
Not Reliable
Suggests that something cannot be trusted to work or last because it's poorly made. They couldn't risk using the flimsy rope to pull up the heavy load.