lightweight

A particular weight class, or member of such, as prescribed by the rules, between that of the heavier welterweight and the lighter featherweight. See Wikipedia for the specifics of each sport.

A particular weight category as prescribed by the rules, separate from an open or heavyweight class.

A competitive weight division as prescribed by the rules, between the heavier middleweight and the lighter featherweight.

One of little consequence or ability.

A person who cannot handle their drink; one who gets drunk on very little alcohol.

"Wait, is this about the other night when you two lightweights totally went on that bender?"

Lacking in earnestness, ability, or profundity.

Having less than average weight.

[…] the Plan incorporates in proper combination every available modern technique, including extensive electrification on the new standard high-voltage a.c. system at a frequency of 50 cycles; main-line diesel traction as a half-way house to electrification; lightweight diesel trains for secondary and branch services; and a smaller wagon fleet doing more work by the use of continuous brakes in conjunction with modernised terminals and marshalling yards.

For example, lightweight construction and Jacobs bogies save weight, and a lighter train uses less power.

Lacking in strength.

With the Gunners far too lightweight in midfield, Mikel Arteta dropped back into a deeper-lying role. This freed Yossi Benayoun to go further forward, a move that helped forge a rare Arsenal chance on 30 minutes when the Israeli released Van Persie, only for the Dutchman's snap-shot to be tipped around the post.

Having a small footprint or performance impact.

To reduce the amount or weight of.

By extending the producer’s responsibility to the product’s disposal (its post-consumer life), issues previously outside the business calculus become of paramount importance. Because a producer knows it will have to bear the cost of collecting and valorizing the product, it must manage a new set of business matters. Can the packaging be lightweighted? Are the materials all recyclable?

The solar photovoltaic array, GPS antennae and telephony antenna all would be lightweighted and integrated into the balloon structure, and the sensor-module would be ruggedized and miniaturized.