"Trifles" is used in Susan Glaspell's Trifles to create verbal irony,which is defined as...
...the saying of one thing and meaning another.
The play is about the unseen Mrs. Wright who is being held for the suspected murder of her husband. The authorities (the men) have come to look for evidence against Minnie Wright. The women have come to gather a few things to take to Mrs. Wright while she is in jail. The idea of "trifles" is introduced as one of the men speaks as to what he considers the hard work of a woman living on a farm:
MRS. PETERS [To the other woman.]
Oh, her fruit; it did freeze. [To the LAWYER.]
She worried about that when it turned so cold. She said the fire'd go out and her jars would break.
Well, can you beat the women! Held for murder and worryin' about her preserves.
I guess before we're through she may have something more serious than preserves to worry about.
Well, women are used to worrying over trifles. [The two women move a little closer together.]
A "trifle" is defined as:
an article or thing of very little value
Hale has just said that everything a woman does to try to keep up with the work on a farm, inside and out, is of little importance. The stage directions note that hearing this, Mrs. Hale and Mrs. Peters move more closely together: for in dismissing what Mrs. Wright does, he has also insulted these women. He sees trifles; the women see the substance of their lives.
Hale represents the viewpoint of a male-dominated society—inferring how unimportant a woman's work is. In that it fills every day of a woman's life, the comment diminishes a woman as she works tirelessly to accomplish things that men take for granted.
The two women symbolize all housewives who struggle to keep up with the demands of days that are long and exhausting. When the County Attorney washes the jelly from his hands, he criticizes the dirt on the towel. Mrs. Hale defends Minnie's housekeeping against his criticism. She explains how hard it is to keep house, especially when the men use towels with dirty hands. Mr. Hale has offended the women by making light of their labors, showing a distinct divide between the world of men and the world of women.
This attitude alienates the women and they slowly come to understand Minnie's painful existence: she has no children; her husband (John) is antisocial and selfish: Hale adds to this understanding...
...I didn't know as what his wife wanted made much difference to John.
Then the women find the birdcage, looking like it has been mauled, and the dead bird wrapped gently in Minnie's sewing box. They realize hands have wrung the bird’s neck. We can infer that—emotionally and perhaps physically—her husband also has brutalized Minnie. The women decide to withhold evidence of the dead bird from the men to protect Minnie.
The "trifles" that the men brush aside are the only things allowed to women. They are anything but trivial to them. The men in the house have the same dismissive attitude as John did. The trifles (as they are called) are the most important things in Minnie's life. The bird would seem to the men to be a trifle, but it is more important to Minnie than anything. At the bird's death, she snaps and kills John.
A final irony is that the women may seem trifle, but they are hardly that. Aware of John's cruelty, Mrs. Hale and Mrs. Peters do all they can to protect Minnie from the men, showing a power the men don't even notice.