If a person contracts COVID and influenza at the same, which leads to a flu infection then it can be termed as a co-infection.
With the onset of winter, the chances of contracting COVID and flu increase significantly. And, now World Health Organisation (WHO) has warned that, there might be a rise in Covid-flu coinfection cases too.
Last week, WHO official Maria Van Kerkhove tweeted that there could be widespread circulation of COVID19 & flu (& other pathogens) this winter.
But, she has specifically urged all not to use the term 'twindemic' to describe the disease are call it infection on infection.