what do economists mean by ipd flows?

Answer 1

Interest, profits and dividends. In a country's balance of payments income paid to its residents and resident businesses by foreigners (including foreign subsidiaries) counts as a plus entry on the current account. Income paid to foreigners is a minus entry.

So if for example IBM UK pays a £100m dividend from its UK operations to its US shareholders, that £100m is income from overseas investment for the United States and a + item on the US IPD account; correspondingly, in the UK balance of paymetns it's a minus item.