What is the meaning of the term "res gestae"?

The term “res gestae” was discussed by Lord Wilberforce in Ratten v. R., [1971] 3 All E.R. 802 (P.C.) at p. 806: The expression ‘res gestae’, like many Latin phrases, is often used to cover situations insufficiently analysed in clear English terms. ... concentration tends to be focused on the opaque or at least imprecise Latin phrase rather than on the basic reason for excluding the type of evidence which this group of cases is concerned with. There is no doubt what this reason is: it is twofold. The first is that there may be uncertainty as to the exact words used because of their transmission through the evidence of another person than the speaker. The second is because of the risk of concoction of false evidence by persons who have been the victim of assault or accident.