This includes amounts earned that aren't in direct relation to your main trading activity. For example selling some bits and pieces on eBay or a penalty paid to you by
a customer or supplier.
Ad-hoc goods sold online through eBay or GumTree.
Penalty paid to you by your client or supplier.
What's not included
Any sales to do with your main trading activity.
Refunds from your suppliers should go against the expense category they were originally allocate against, not in to other income.
How is it taxed?
These amounts are taxed as you show them in your accounts. You need to make sure the level of other income is low, otherwise the HMRC may question you on what your main trading activity really is.
Where this income starts to equal or exceed your main source of income we recommend you take tax advice to ensure you may not be effectively changing the nature of your company's trade and risk accidentally losing rights to historic losses/allowances.