To speculate means
i) to guess or assume about something when not many things are known
ii) to invest money in shares that could earn large profit
but also involves a lot of risk. As Section 43(5) in The Income- Tax Act , “speculative transaction” means a transaction in which a contract for the purchase or sale of any commodity, including stocks and shares, is periodically or ultimately settled otherwise than by the actual delivery or transfer of the commodity or scrips.