In festo Ss Michaelis, Gabrielis, et Raphaelis, Archangelorum -- a.k.a. "Michaelmas"

 

In the traditional Roman Rite this is the feast of St Michael the Archangel only as all three archangels used to have their own separate feast days.  Hence, today was just "Michaelmas".  In the Book of Common Prayer it's St Michael and All Angels. The Novus Ordo compromised - more than St Michael but less than All: it celebrates the Feast of St Michael, St Gabriel, and St Raphael.    The Ordinariates went along with the N.O. and just name the three archangels.

Chambers Book of Days points out that

In England, it is one of the four quarterly terms, or quarter-days, on which rents are paid, and in that and other divisions of the United Kingdom, as well as perhaps in other countries, it is the day on which burgal magistracies and councils are re-elected. The only other remarkable thing connected with the day is a widely prevalent custom of marking it with a goose at dinner.

In fact, it seems that having a goose for dinner was a harbinger of good fortune for the coming year.  Chambers explains:

 This is also an ancient practice, and still generally kept up, as the appearance of the stage-coaches on their way to large towns at this season of the year amply testifies. In Blount's Tenures, it is noted in the tenth year of Edward IV, that John de la Hay was bound to pay to William Barnaby, Lord of Lastres, in the county of Hereford, for a parcel of the demesne lands, one goose fit for the lord's dinner, on the feast of St. Michael the archangel. Queen Elizabeth is said to have been eating her Michaelmas goose when she received the joyful tidings of the defeat of the Spanish Armada. The custom appears to have originated in a practice among the rural tenantry of bringing a good stubble goose at Michaelmas to the landlord, when paying their rent, with a view to making him lenient. In the poems of George Gascoigne, 1575, is the following passage:

And when the tenants come to pay their quarter's rent,

   They bring some fowl at Midsummer, a dish of fish in Lent,

At Christmas a capon, at Michaelmas a goose,

    And somewhat else at New-year's tide, for fear their lease fly loose.'

We may suppose that the selection of a goose for a present to the landlord at Michaelmas would be ruled by the bird being then at its perfection, in consequence of the benefit derived from stubble-feeding. It is easy to see how a general custom of having a goose for dinner on Michaelmas Day might arise from the multitude of these presents, as land-lords would of course, in most cases, have a few to spare for their friends. It seems at length to have become a superstition, that eating of goose at Michaelmas insured easy circumstances for the ensuing year. In the British Apollo, 1709, the following piece of dialogue occurs:

'Q: Yet my wife would persuade me (as I am a sinner)

To have a fat goose on St. Michael for dinner:

And then all the year round, I pray you would mind it,

I shall not want money—oh, grant I may find it!

Now several there are that believe this is true,

Yet the reason of this is desired from you.

A: We think you're so far from the having of more,

That the price of the goose you have less than before:

The custom came up from the tenants presenting

Their landlords with geese, to incline their relenting . . . 

You can find the whole article here